The present invention relates to therapeutically active iron-containing species including parenteral hematinic pharmaceuticals. For purposes of the present invention a “hematinic” means a compound or composition comprising iron in a form that tends to increase the amount of hemoglobin in the blood of a mammal, particularly in a human. While such compounds can be broadly characterized as iron-carbohydrate complexes, which can include dextrans, the present invention is directed to the generic subclass known as iron-saccharidic complexes and includes such species as sodium ferric gluconate complex in sucrose (SFGCS), ferric hydroxide-sucrose complex (FHSC) and/or others characterized as iron saccharates. For purposes of the present invention, such active iron-containing species are referred to generically as iron-saccharidic complexes or active hematinic species (AHS). The term “complex” may have alternate meanings in various contexts in the related art. In one aspect, the term complex may be used to describe the association between two or more ions to form a relatively low molecular weight non-polymeric composition which exists singly under a given set of conditions. This type of complex has been referred to as a “primary complex”. An alternate manner in which this term is used is to describe an association or agglomeration of a plurality of primary complexes into a large macromolecule, or “secondary complex.” For purposes of the present invention, the latter agglomerates are also referred to herein as macromolecules. For the purposes of the present invention, such macromolecules or secondary complexes are identified as “complexes” and are referred to simply as complexes. As an example of the above distinction, ferrous gluconate is a composition comprising divalent iron ions and gluconate anions. A divalent iron ion and two gluconate anions form a primary complex of relatively low molecular weight (about 450 Daltons) and primary complexes of this type do not become agglomerated into macromolecules when dissolved into an aqueous medium. Ferrous gluconate, therefore, is a not composition which falls within the scope of the term “complex” herein. Ferric gluconate, however, does exist as a complex as that term is used herein because primary complexes of trivalent iron ions and gluconate anions agglomerate to form large macromolecules (and can have molecular weights of from about 100,000 to about 600,000 Daltons, or more). Several embodiments of therapeutically active ferric iron compounds are commercially available, as will be described below. For purposes of the present invention, the term “excipients” means non-hematinically active components, including synthesis reaction by-products and unreacted starting materials, degradation by-products, diluents, etc., present in admixture with therapeutically active iron-containing species such as iron-saccharidic complexes. Such excipients can include one of more sugar, such as sucrose, that may be present in combination with the AHS following synthesis, as an unreacted or partially reacted component, or added to the AHS in the course of preparing a parenteral composition, e.g., commercially available parenteral iron compositions as described below.
Iron deficiency anemia is a blood disorder that can be treated using various therapeutic preparations containing iron. These preparations include simple iron salts such as ferrous sulfate, ferrous gluconate, ferrous fumarate, ferrous orotate and others. Various low molecular weight iron, Fe(III), compounds intended for use as oral or nutritional supplements are known. Such low molecular weight compounds are only useful as oral supplements, since the introduction of materials having high unit concentrations of iron directly into the bloodstream by injection would be contraindicated and could be toxic. In contrast, the compounds of the present invention, intended for parenteral use, have lower iron concentrations and can be used parenterally. For purposes of the present invention, parenteral means introduced into the body by some other means than through the gastrointestinal tract; for example, by intradermal, subcutaneous, intramuscular, intravenous, intramedullary, intra-articular, intrasynovial, intraspinal, intrathecal or intracardiac injection or infusion.
If the use of such orally administered substances fails to ameliorate iron deficiency, the next level of treatment includes parenteral iron administration. Depending on a patient's clinical status, parenteral administration of polyglucan or dextran-linked iron may serve as an effective therapeutic iron-delivery vehicle. Intramuscular injection or intravenous routes may be used to administer these iron dextrans; commercial examples of such products include those having trade names such as “Imferon”, and “INFeD”. Various clinical conditions that require parenteral iron have shown the practical hematinic value of iron dextrans. The use of iron dextrans is tempered by idiosyncrasies in their synthesis, manufacturing and patient responses such as hypersensitivity. These effects may be exhibited as a severe allergic response evident as anaphylaxis or symptoms as minor as transient itching sensations. Whether such allergic or other adverse effects are due to individual patient sensitivity to the active ingredient or to byproducts, impurities or degradation products in the parenteral solution has not been established.
As an alternative to iron dextrans, iron-saccharidic complexes are regarded herein as non-dextran hematinics. Whereas the iron dextrans comprise polymerized monsaccharidic residues, the iron-saccharidic complexes of the present invention are characterized by the substantial absence of such polymerized monosaccharides. Iron-saccharidic complexes are commercially available, for example, under the tradename Ferrlecit, which is identified as sodium ferric gluconate complex in sucrose (SFGCS). The manufacturer states that the structural formula of the product is considered to be [NaFe2O3 (C6H11O7) (C12H22O11)5]n, where n is about 200, and as having an apparent molecular weight of 350,000±23,000 Daltons. However, it is noted that, based on the published structural formula just recited, the formula weight should be significantly higher, 417,600 (although, as published, the formula is difficult to accurately interpret). Furthermore, the commercial hematinic composition comprises 20% sucrose, wt./vol. (195 mg/mL) in water. The chemical name suggests that therapeutic iron (Fe) in this form is pharmacologically administered as the oxidized ferric form Fe(III) as opposed to the reduced ferrous Fe(II) form. Owing to the charged oxidation state of Fe(III) it has been suggested that gluconic acid (pentahydroxycaproic acid, C6H12O7) also exists in a coordination complex or ligand form in a sucrose solution. For purposes of the present invention it is to be understood that the chemistry of gluconate, whether held in a ligand complex with Fe(III) or not, does not exempt it from interactions with other carbohydrates that may be present, such as sucrose. Thus, use of the term iron-saccharidic complex will be understood to indicate the existence of a nonspecific and imprecise structure where ionized gluconic acid (gluconate) and sucrose molecules are tenuously associated by various bonding interactions to give a molecular scaffolding that incorporates Fe(III). Another non-dextran hematinic of the present invention is compositionally described as ferric hydroxide-sucrose complex (FHSC). This parenteral hematinic is commercially available under the tradename “Venofer”. As with SFGCS, the descriptive name suggests a form of ferric iron, Fe(III), that is present in a spatial complex with sucrose or some derivative of sucrose. Therefore, non-dextran, iron-saccharidic complexes of the present invention include SFGCS, FHSC and mixtures thereof. These iron delivery vehicles include an iron-containing structural complex that, for purposes of the present invention, is designated the active hematinic species (AHS).
For purposes of the present invention, the term AHS is used interchangeably with iron-saccharidic complex, saccharidic iron delivery vehicle, and iron saccharate. The term “saccharate” or “saccharidic” is employed to generically describe iron atom interactions with another individual molecule or its polymers that display a saccharose group structurally identified as—CH(OH)—C(O)—
The simplest occurrence of the saccharose group is where the two terminal positions in a standard Fischer molecular projection model of a molecule appear as an ald- or a keto-group respectively designated as:(—CH(OH)—CHO) or (—CHO—CH2OH).
This nomenclature format is also described in Zapsalis, C. and R. A. Beck, 1985, “Food Chemistry and Nutritional Biochemistry,” Chapter 6, John Wiley & Sons, pp. 315-321 (incorporated herein by reference to the extent permitted). Such groups and their first oxidation or reduction products occur in molecules recognized as monosaccharides that contain carbon atoms with hydrogen and oxygen in the same ratio as that found in water. By way of example, the aldose sugar known as glucose would have gluconic acid as a first oxidation product and glucitol, also known as sorbitol, as a first reduction product. Both the original monosaccharide represented by the model of glucose and its possible reaction products retain evidence of the characteristic saccharide group in an oxidized or reduced form. While these structural variations exist, both remain recognized as monosaccharides and carbohydrates. In practical nomenclature, the oxidized version of the saccharose group exhibits a carboxyl group which under the appropriate pH conditions will allow it to ionize according to its unique ionization constant and pKa value. When ionized, the oxidized saccharose group is denoted as a “saccharate” or it can be generically described as a saccharidic acid where the ionizable proton remains with the oxidized saccharose group. If the ionized carboxyl group of the saccharose group is associated with a cation such as sodium, a saccharidic acid salt is formed. For example, oxidation of glucose gives gluconic acid and the sodium salt of this saccharidic acid is sodium gluconate. Similarly, where a ferrous (FeII) cation is electrostatically associated with the carboxyl group of gluconic acid, ferrous gluconate results. Monosaccharides that are aldoses commonly undergo oxidation to give their saccharidic acid equivalents or, when ionized, monosaccharate forms may interact with selected cations having valence states of +1 to +3. Glyceraldehyde is the simplest structure that demonstrates such an ald-group while dihydroxyacetone serves as a corresponding example of a keto-group. Practical extensions of such structures with six carbon atoms account for the descriptive basis of two carbohydrate classifications, one form being aldoses and the other ketoses. Aldoses and ketoses are respectively represented by monosaccharides such as glucose or fructose. With many possible intra- and intermolecular reaction products originating from monosaccharides, including the glucose oxidation product known as gluconic acid, efforts to complex iron with saccharates can produce an AHS. For purposes of the present invention, AHS is considered to be a more chemically complex embodiment of hematinic iron than suggested by the generic descriptor sodium ferric gluconate complex in sucrose (SFGCS) or ferric hydroxide-sucrose complex (FHSC), and therefore, designations including iron-saccharidic complex or saccharidic-iron delivery vehicle or saccharidic-iron are used interchangeably with AHS. Consequently, intra- and inter-molecular reactions or associations from reactions of monosaccharides with iron during hematinic syntheses can coincidentally produce a wide variety of structural species with hematinic properties that are encompassed within the present invention.
Typically iron-dextrans are provided for delivery of up to 100 mg Fe(III)/2.0 milliliter (mL) of injectable fluid, whereas iron-saccharidic complexes can provide 50-120 mg of Fe(III)/5.0 mL volume as commercially prepared in a single dose. As made, many of these iron-saccharidic complex products contain 10-40% weight-to-volume occurrences of non-hematinic excipients as well as synthesis reaction by-products.
While some hematinic agents have an established compendial status under the aegis of the United States Pharmacopoeia (USP) or National Formulary (NF), iron-saccharidic complexes have no acknowledged compendial reference, standardized molecular identity characteristics or documented molecular specificity unique to the active hematinic species. This suggests that the iron-delivery vehicle in non-dextran hematinics such as SFGCS or FHSC has not previously been adequately purified and separated from manufacturing excipients so as to permit detailed characterization. Consequently, there has not been developed a benchmark reference standard or an excipient-free analytical quality control index capable of characterizing one desirable hematinic agent from others having uncertain characteristics. Since the 1975 merger of the USP with the NF to produce the USP-NF compendial guidelines for drugs, standard identities and analytical protocols have been developed for over 3,800 pharmaceuticals while 35% of marketed pharmaceuticals are still not included in the USP-NF. Hematinic pharmaceuticals such as SFGCS and FHSC fall within this latter category. This issue has been recently addressed in “Raising the Bar for Quality Drugs”, pp. 26-31, Chemical and Engineering News, American Chemical Society, Mar. 19, 2001. As in the case of immune and anaphylactic responses elicited by specific antigens, a fine line of molecular specificity and compositional differentiation can separate a no-adverse-effect level for one hematinic's active molecular structure and excipients from another that may induce such adverse reactions. Thus, there is a need to identify features that document one hematinic's safe and effective characteristics from others where little is known about the iron-delivery vehicle, excipients representing synthesis reagent overage or byproducts of hematinic synthesis reactions. Furthermore, there are no long-term detailed sample archives or data using modern analytical instrumentation that meaningfully characterize the chemical nature of even the safest parenteral iron-saccharidic complexes. Moreover, correlation between variations in normal hematinic manufacturing conditions and their consequential effects identifiable as changes in the chemical structure of a released pharmacological agent have not been identified. The methods of the present invention can address such issues.
The present invention can also provide an analytical basis for a routine protocol in order to fingerprint and characterize iron-saccharidic complexes such as SFGCS, FHSC and others as well as discriminate between competing products and structural transformations exhibited by an individual product.
The need to characterize an AHS is also reflected in the quality control demands of manufacturing processes, particularly where endothermic conditions and heat transfer issues can affect final product quality. Whatever the proprietary synthesis process, possible heat-driven or Strecker reaction byproducts in some commercially released non-dextran products suggest that hematinic product formation is contingent on at least some controlled heat-input during the course of manufacturing. Such excipients would not occur if process temperatures less than about 50° C. were unnecessary. It follows then, that product quality is related, to some extent, to issues of heat transfer rates and duration of heat exposure. Where products are especially sensitive to heat processing conditions, knowledge of excipient profiles can also provide significant insight to the product quality of the active pharmacological substance. In other words, monitoring the safe and effective pharmacological agent can also be indicated by the nature and constancy of excipient occurrence in a drug as released into the marketplace.
Analytical studies on iron-saccharidic complexes, including AHS and its coexisting excipients are hampered by factors of low concentration, molecular interactions, over-lapping analytical signals and so on. For both SFGCS and FHSC, analytical challenges include high concentrations of hydrophilic excipients, including excess reactants and reaction and post-reaction byproducts, from which their respective AHS's have not previously been isolated or reported in terms of their individual properties. Reference standards for pharmaceuticals need to abide by practical protocols that are routinely achievable using methods that are analytically discriminating and able to be verified and validated. There is a continuing need for such methods and application of the present invention can facilitate compliance with such protocols as well as verifying manufacturing consistency and product stability.